I. Field of the Invention
The present invention relates to medical devices, and, more particularly, to such medical devices with an advantageous coating.
II. Description of Prior Art
Medical devices are used to treat human tissue in many ways. Many such devices are elongated with one end adapted to be held, either by hand or by a mounting, with the other end being comprised of a parent metal and adapted to contact or otherwise interact with human tissue. By way of example, a needle has a proximal end adapted to be mounted to a syringe cannula for injection or withdrawal of fluids from a body, or to a length of flexible tubing such as in an IV catheter. In either case, the metal distal end is adapted to be inserted into and through human skin and blood vessels for passage of fluids therethrough. Similarly, a scalpel has a proximal end adapted to be held by a surgeon""s hand in use and a distal end with a metal blade adapted to interact with tissue by cutting same, for example. One specialized type of medical instrument is an electrosurgical knife or RF scalpel which is used to cut or cauterize tissue. Typical of such instruments is that they use an elongated medical device referred to as an active electrode or tip, sometimes also referred to as a Bovie tip, to contact and cauterize the tissue. The tip is electrically conductive and cooperates with another conductor, such as a dispersive electrode (monopolar) or an adjacent electrode or tip (bipolar), to allow current flow at the site to be treated. These tips have a proximal end adapted to be mounted to the knife, with the distal end defining an active metal electrode area to cut or cauterize tissue of interest.
The various medical devices must cut into and/or slide along the tissue and so it is desirable to avoid the tendency of the distal end to stick on or to the tissue. By way of example, with the Bovie tip, a surgeon must be able to move the active electrode area along the tissue without tissue or carbonaceous remains from burnt tissue sticking thereto. Several proposals have been made to provide a non-stick surface to the active electrode area, however none are entirely satisfactory. For example, the tip may be coated with PTFE or Teflon(copyright) coating. Teflon(copyright) material is not always easy to apply and may vaporize in use exposing the patient or surgeon to certain risks. Additionally, the Teflon(copyright) coating is not a good conductor. Consequently, it has been the practice to expose the edges of the tip rather than provide the edges with the desirable nonstick coating. That, in turn, has limited the ability of the tip to conduct electricity uniformly across the surface.
Other examples are to plate the tip with platinum or coat the tip with conductive ceramic. The plating or coating process can be quite complex and costly. Indeed, platinum is itself quite costly. Relatedly, ceramics can be quite brittle, thus exposing the patient to risk of injury if pieces of ceramic chip or break off from the tip. One further proposal has been to apply a conductive silver and glass frit to the parent metal of the electrosurgical knife tip, and then to sinter the frit to form a precursor. A monofunctional silane is applied over the sintered frit, with the silane filling into the microscopic interstores formed by the frit, and with any excess wiped away so as to be certain to expose the conductive frit. The sintered frit is said to be necessary because the monofunctional silane would otherwise interfere with the conductivity of the knife tip. The requirement to first apply and sinter a silver and glass frit is undesirable.
Other medical coatings, particularly for polymeric and/or other non-metallic surfaces, have proposed to, use silane as a precursor or cross-linking agent to a different, additional coating or layer to be added over the medical device. Typical of the precursor silanes is that they are also monofunctional silanes, may be a polymer as applied, and/or may include halogens or metal in the silane composition. Those attributes combined may be useful for some medical devices, but are considered to be undesirable for application to the parent metal of medical devices. In the case of electrosurgical knife tips in particular, presence of reactive material like halogens can be deleterious in use. Moreover, the use of silane as a precursor thus requires a yet further application of a different coating material, with added costs, handling and thickness that may be undesirable for the metal, tissue-contacting end of medical devices.
There is thus a need to provide a medical device with a low cost, reliable non-stick coating for the metal, tissue-contacting distal end, and in the case of electrosurgical knife tips with desirable conductive properties on the active electrode area, but without the drawbacks associated with platinum plating, ceramic coating, Teflon(copyright) coating, or a sintered frit precursor.
The present invention provides a low cost, reliable non-stick coating for the metal, tissue-contacting distal end of medical devices, and in the case of electrosurgical knife tips also affords desired conductivity, without the drawbacks associated with platinum plating, ceramic coating, Teflon(copyright) coating, or a sintered frit precursor. To this end, and in accordance with the principles of the present invention, a medical device has a proximal end portion adapted to be held and a distal end portion comprised of a parent metal and which is adapted to contact and/or interact with tissue, with at least a selected portion or aspect or all of the distal end portion, such as the active electrode area of an electrosurgical knife tip, provided with a coating consisting essentially of a silane directly applied to the parent metal at the surface of the distal end. Alternatively, or additionally, the silane coating may be a polyfunctional silane, may be an in-situ polymerized monomeric silane (i.e., it is monomeric or uncross-linked as applied and then polymerized in-situ on the device), and may further be halogen-free (particularly where the medical device is an electrosurgical knife tip). Advantageously, the coating does not include metal in the silane as applied. Silane is inexpensive compared to platinum, and possibly even when compared to Teflon(copyright) or ceramic materials, and application as the sole coating avoids the drawbacks of applying a sintered frit precursor or application of subsequent coatings with different materials. The silane may also be readily applied in liquid form, and then easily heated to form a desired stable and non-brittle coating, without the complications typical of platinum plating or problems encountered in coating with Teflon(copyright) or ceramic materials. The resulting silane coating displays both non-stick and/or conductive properties as are desired for the metal, tissue-contacting ends of medical devices, and particularly electrosurgical knife tips.
The distal end portion of such medical device can take many shapes, including flat, cylindrical, knife edge or blade-like, ball or spherical, paddle, hook, needle, and round loops, by way of example. One common electrosurgical knife tip, known as a Bovie tip, has a cylindrical shaft at the proximal end supporting a flattened active electrode area at the distal end. The electrode area has flat surfaces which, in cross-section, may present canted flat walls. The flat surfaces join at lateral peaks or edges and the canted walls of the flat surfaces may join at peak edges. Advantageously, for Bovie tips, the silane extends over at least the flat surfaces, and may further advantageously extend over the edges as well. Thus, even the edges have a non-stick coating yet are still able to conduct as desired for proper operation of the Bovie tip. For other shapes of the active electrode area of the Bovie tip, the silane coats some or all of the active electrode area which is intended to contact or interact with the tissue.
By virtue of the foregoing, there is thus provided a low cost, reliable non-stick coating for the metal, tissue-contacting distal end of medical devices, and in the case of electrosurgical knife tips also affords desired conductivity, without the drawbacks associated with platinum plating, ceramic coating, Teflon(copyright) coating, or a sintered frit precursor. These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.